clarify complexity limits (#872)

* clarify complexity limits * Update fundamentals-limitations.md * Update fundamentals-limitations.md * Update release-notes-new-features39.md * Update release-notes-upgrading-changes39.md Co-authored-by: ansoboleva <93702078+ansoboleva@users.noreply.github.com>

Author: jsteemann

3.10/aql/fundamentals-limitations.md

@@ -12,7 +12,9 @@ The following hard-coded limitations exist for AQL queries:
  internal/anonymous query variables, e.g. for intermediate results.
  Subqueries also require result registers.
 - An AQL query cannot have more than _4000_ execution nodes in its initial
- query execution plan.
+ query execution plan. This number includes all execution nodes of the
+ initial execution plan, even if some of them could be
+ optimized away later by the query optimizer during plan optimization.
 - An AQL query cannot use more than _2048_ collections/shards.
 - Expressions in AQL queries cannot have a nesting of more than _500_ levels.
  As an example, the expression `1 + 2 + 3 + 4` is 3 levels deep

3.9/aql/fundamentals-limitations.md

@@ -12,7 +12,9 @@ The following hard-coded limitations exist for AQL queries:
  internal/anonymous query variables, e.g. for intermediate results.
  Subqueries also require result registers.
 - An AQL query cannot have more than _4000_ execution nodes in its initial
- query execution plan.
+ query execution plan. This number includes all execution nodes of the
+ initial execution plan, even if some of them could be
+ optimized away later by the query optimizer during plan optimization.
 - An AQL query cannot use more than _2048_ collections/shards.
 - Expressions in AQL queries cannot have a nesting of more than _500_ levels.
  As an example, the expression `1 + 2 + 3 + 4` is 3 levels deep

3.9/release-notes-new-features39.md

@@ -297,7 +297,13 @@ The following limits have been introduced:
  The expression recursion is limited to 500 levels.
 - a limit for the number of execution nodes in the initial query
  execution plan.
- The number of execution nodes is limited to 4,000.
+ The number of execution nodes in the initial query execution plan is 
+ limited to 4000. This number includes all execution nodes of the
+ initial execution plan, even if some of them could be
+ optimized away later by the query optimizer during plan optimization.
+
+AQL queries that violate these limits will fail to run, and instead abort 
+with error `1524` ("too much nesting or too many objects") during setup.
 
 ### RocksDB block cache control
 

3.9/release-notes-upgrading-changes39.md

@@ -74,7 +74,13 @@ The following limits have been added:
  is 3 levels deep `1 + (2 + (3 + 4))`.
  The recursion of expressions is limited to 500 levels.
 - a limit for the number of execution nodes in the initial query 
- execution plan. The number of execution nodes is limited to 4,000.
+ execution plan. The number of execution nodes is limited to 4000.
+ This number includes all execution nodes of the initial execution plan, 
+ even if some of them could be optimized away later by the 
+ query optimizer during plan optimization.
+
+AQL queries that violate these limits will fail to run, and instead abort 
+with error `1524` ("too much nesting or too many objects") during setup.
 
 Also see [Known limitations for AQL queries](aql/fundamentals-limitations.html).